Field of the Invention
The present invention relates to a toner, a developing device, and an image forming apparatus for use in electrophotography and an image forming method for visualizing an electrostatic charge image.
Description of the Related Art
In recent years, the way in which copying machines and printers are used has changed from “one machine for a plurality of people” to “one machine for one person”. Accordingly, further reduction in size needs to be achieved while ensuring a long life and high image quality. In this regard, it is effective to reduce the size of a process cartridge in which a developer is stored and to reduce the size of a fixing device mounted on a main body. One of effective means for reducing the size of the process cartridge is the use of a cleanerless system. Since the cleanerless system does not have a cleaning blade or waste toner box, it can greatly contribute to the size reduction of the main body.
In the cleanerless system, the toner remaining on an electrostatic latent image bearing member after the transfer is collected by a toner carrying member in the developing device and sent to a developing step again. As compared with a configuration having a cleaning blade, the stress applied to the toner is increased, and cracking or crushing of the toner particle may occur.
The occurrence of cracking and crushing of the toner particle is significant particularly when the members such as a toner carrying member and a regulating blade become hard under a low-temperature and low-humidity environment. In this case, the particle size distribution is widened and rubbing between the toner carrying member and the blade is unlikely to produce sufficient charging. As a result, the so-called fogging, that is a phenomenon in which a toner having a low charge quantity is developed in a non-image area on the electrostatic latent image bearing member, is likely to occur. In order to suppress such a fogging phenomenon, it is necessary to improve further the brittleness of toner particles.
The reduction in size of the fixing device mounted on the main body is considered to be another effective means for reducing a printer in size.
In the case of film fixing, simplification of a heat source and device configuration is easy and can be readily applied to reduce the fixing device in size. However, since film fixing generally uses a small amount of heat and a light pressure, heat may not be sufficiently transferred to the toner. Also, in recent years, printers are often used under various environments all over the world, and particularly under a room-temperature and high-humidity environment, heat is consumed by moisture and the amount of heat given to the toner is further reduced.
Under these conditions, when a solid image is printed, sufficient heat is not transferred to the toner, the toner is hardly melted, and the adhesion between the paper and the toner or between the toner particles is deteriorated. As a result, an image defect (referred to hereinbelow as “white spots”) occurs in which a part of the solid image blurs out white. Where the melt viscosity of the toner is lowered to solve this problem, the toner particles are cracked or crushed as described above, or density unevenness of the fixed image is likely to occur, in particular, when paper having low smoothness is used.
Therefore, in film fixing, a toner that can be fixed with a small amount of heat and light pressure becomes necessary.
It follows from the above that it is appropriate to use a cleanerless system and film fixing to reduce the printer in size. For that purpose, a toner that can be fixed with a small amount of heat and light pressure, while suppressing cracking and crushing of the toner particle under a low-temperature and low-humidity environment is required, and various methods for improving toners have been suggested to solve these problems.
In Japanese Patent Application Publication No. 2004-295105, both charging stability and fixing performance are achieved by using a toner in which a styrene acrylic resin and a polyester resin are dispersed at a micro level.
Further, Japanese Patent Application Publication No. 2011-145587 discloses many examples in which both development stability and fixing performance are achieved by finely dispersing a crystalline resin having a toner plasticizing effect in the toner.
Japanese Patent Application Publication No. 2015-152703 describes a toner in which a toner particle includes a binder resin containing an amorphous resin (A) and an amorphous polyester resin (B), and a colorant, wherein the amorphous polyester resin (B) is dispersed as a domain phase in a matrix phase including the amorphous resin (A). It is indicated that a number average domain diameter has a value within a specific range in an observation image of the toner particle cross section.